1. Field of the Invention
The present invention relates to a cheese process vat. More specifically, the present invention relates to generally horizontal cheese process vats for producing cheese. The present invention relates to a single-shaft cheese process vat having a shaft assembly preferably including a generally horizontal shaft and substantially balanced agitator panels. In preferred embodiments, the panels are balanced in both weight and surface area around the centerline of the shaft. The present invention relates also to methods for making cheese and cheese-like products in the same.
2. Description of the Related Art
In the 1970's, a number of companies manufactured enclosed vertically agitator shafted vats for making cheese and cheese-like products. These enclosed vats improved upon inconsistent cheese making results generally noted in the open cheese making vats that were common in those days. The enclosed vats also reduced the risk of foreign material contamination and the interior could be automatically cleaned with automatic, clean-in-place (CIP) spray systems. Initially, these vats had vertical agitator shafts. Such vats include the Damrow® Double O™ Vat and the Stoelting® Vertical Vat.
In the late 1980's, cheese process vats having horizontal agitator shafts were introduced. Known horizontal agitator shaft cheese process vats, such as that disclosed by Jay (U.S. Pat. No. 4,989,504), are dual horizontal agitator shaft cheese process vats that are believed to provide considerably improved product yields as compared to the prior vertically agitator shafted vats.
Cheese process vats have also been made having a single horizontal agitator shaft. Previous cheese process vats having single horizontal agitator shafts typically have a majority of their blade clusters or agitator panels on one side of the agitator shaft with blade panels generally confined to about 100° or less of the full 360° radius of the agitator shaft, creating a substantially unbalanced weight distribution with respect to the placement of the agitator panels within the agitator shaft assembly. Such vats include the Tebel OST, the Wincanton and the Stoelting single agitator shaft cheese process vats.
In these vats, during the initial stages of cutting the coagulum, the entire mass of coagulum has a tendency to rotate with the agitator shaft assembly. To compensate for this rolling/rotating action, it is usually necessary to increase the speed of the agitator shaft assembly, which is believed to negatively influence yield, by shattering the coagulum, thus allowing fat release and creation of cheese fines that are drained out of the curd with the whey when the whey is separated from the cheese curds. Further, if a horizontal agitator shaft assembly has a substantially unbalanced weight distribution with respect to the placement of the agitator panels along the agitator shaft, the motor, speed reducer and bearings experience uneven loads as the agitator shaft rotates. The loading along the shaft will generally alternate from a high positive load to one that might be called a free fall, regenerative or negative load. This can cause uneven wear and premature failure of the above mentioned parts.
Known methods of attaching blade clusters or agitator panels to the agitator shaft include welding the agitator panels to stubs located on the main agitator shaft. The blunt edges of the stubs during the cutting phase can damage the coagulum enough to negatively affect product yield.
The original enclosed cheese making vats employed vertical agitator shafts and therefore, did not require a sophisticated water-tight and sanitary seal assembly. The agitator shaft came through an opening in the top of the vessel, which was always above the level of the liquid. With the advent of cheese making vats with horizontal agitator shafts, however, it became necessary to seal the agitator shaft so milk or product would not leak as both ends of the agitator shaft are typically below liquid level during cheese making operations. Under rules promulgated by the USDA, it also became necessary to provide a suitable system to clean the seal assembly and, as further required by the USDA, provide a leak detection port which is open to the floor during the production of cheese. Existing cheese process vat seals consist of a combination shaft seal and face seal molded into one unit such as that disclosed by Jay (U.S. Pat. No. 4,861,044). Typically, the cleaning/sanitizing solution is pumped, through a hole that is molded into the seal between the shaft seal and the face seal.
Testing and evaluating the cheese making performance is contingent on the cheese making process. The cheese making process is made up of numerous steps that change for each type of cheese. Cheese making steps generally include, but are not limited to the following:
First, the sanitized vat is filled with fluid milk and combined with other cheese constituents like calcium, a starter culture a rennet solution and a coloring agent. As the cheese process vat is filling, the agitator shaft assembly automatically starts agitating the fluid milk when the milk fill weight reaches a first stir set point. During the “fill” step, other actions take place, including heating the milk in the vat body, if the milk temperature is not at a required set point.
To add any desired coloring agent, appropriate valves are opened and a color pump generally starts to add a coloring agent, preferably annatto, to the milk when the milk fill weight reaches a preset point. The coloring agent is metered into the milk.
When the milk fill weight reaches another preset point, another set of valves are opened and a pump begins to pump a starter culture into the milk. The starter is generally a bacterial culture in a medium such as milk that is added to enhance flavor and lower pH. Food colorings, calcium and the like may also be added at this point.
Once the vat is full of fluid milk, a modern, programmed cheese process vat will generally advance to a “stir” step commonly referenced as a “rennet stir” step. Rennet solutions include proteolytic enzymes that promote coagulation of the milk when the enzymes react with casein micelles to produce casein proteins that bind together to form a coagulum that is a protein matrix in which a portion of the milk fat is retained. Once the operator is aware of the appropriate time to add the rennet solution and operator initiates a programmed addition sequence, the agitator shaft will generally ramp up to a programmed agitation speed in a stir mode.
Known methods of introducing the rennet solution are known to include manual addition using a pail from the top of the vat, spraying over the top of the surface of the milk using spray nozzles or a gravity feed orifice from an overhead manifold.
Following the addition of the rennet solution, the agitator shaft assembly rotation speed is generally increased to a further programmed speed in the stir mode/direction to thoroughly mix the rennet into the fluid milk. In an attempt to obtain a homogeneous mixture, in which the rennet is evenly distributed to every part of the fluid milk within the vat body, the contents of the vat are often agitated aggressively. This can be counter productive, however, as the coagulum may not set as well under such conditions. After this step is timed out, the cheese process vat advances to an “anti-swirl” step in which the direction of the rotation of the agitator panels is reversed.
The “anti-swirl” step helps to slow down the action of the milk rotating in one direction. The agitator shaft assembly will then begin a cut mode at high RPMs and gradually reduce the agitating speed until stopped. After this step is timed out, the cheese process vat advances to a “set” step in which the casein matrix is allowed to set or coagulate.
The agitator shaft assembly does not rotate in the “set” step. In the “set” step, the milk protein coagulates while the agitator shaft assembly idles to permit the coagulum to form. After the programmed set time expires, the operator will check the set. When the set is ready, the operator will initiate a series of “cut” steps.
In the “cut” steps, the agitator shaft assembly gradually ramps up to a programmed speed in which the coagulum is cut into individual cheese curd matrices (cheese curd). After these steps are timed out, the cheese process vat advances to a “heal” step.
In the “heal” step, the agitator shaft assembly does not rotate. This step allows the outer skin or “shell” of the curd to develop in order to reduce “bleeding” of fat and moisture from the curd. After this step is timed out, the cheese process vat advances to a “forwork” step.
In the “forwork” step, the agitator shaft ramps up in a selected cut or stir mode. In this step, the curd is gently stirred at a relatively slow agitation speed. After this step is timed out, the cheese process vat advances to a “cooking” step.
In the “cooking” step, the agitator shaft assembly increases up to a programmed speed in the stir or cut direction. A vat steam shut off valve or hot water shut off valve generally opens to permit steam or hot water to circulate in the outer jacket surrounding the interior of the vat body. An intermittent agitating time parameter is available to help keep curd from knitting together at low agitator shaft assembly speeds. The “cooking” step will not advance until both the time and temperature required by the program are met. The cheese process vat will then advance to a “predraw/settle” step once cooking is complete.
In the “predraw/settle” step, the agitator shaft assembly does not run. The agitator shaft assembly is parked in a vertical position. Curd gradually drops into the whey fluid mixture in the vat body because it is denser than the whey that remains after the cheese curd is formed. After this step is timed out, the cheese process vat advances to a “predraw” step.
In the “predraw” step, the agitator shaft assembly does not run as it remains parked in the vertical position. A predraw valve opens and a predraw pump starts to remove whey from the vat body. Once a set amount of whey is drawn off, the predraw pump shuts off and the predraw valve closes.
Next, during an “end stir” step, the agitator shaft assembly increases to a programmed speed in the stir direction. The “end stir” step ends and a “curd transfer” step begins once the programmed time for the “end stir” step has elapsed.
Finally, in the “curd transfer” step, appropriate valves are opened and curd pumps will pump the curd and any remaining whey out of the vat body to finishing areas. During the curd transfer, the agitator shaft assembly speed increases and has the option to be in a “stir” mode or a “cut” mode.
Once empty, the interior of the vat is usually cleaned automatically with the use of internally mounted spray devices that are part of a sanitizing system generally called a “clean in place” (CIP) system.
Although cheese making has advanced significantly in the past 20 to 30 years, it will be appreciated that a cheese process vat that increases cheese yield is needed in order to make automated cheese making more efficient and less reliant upon operators that possess the knowledge of the “art” of cheese making. What is also needed is a cheese process vat that is easier to clean, easier to operate without undue wear on parts and easier to operate in ways that produce cheese more efficiently. What is further needed is a cheese process vat with a shaft seal assembly that is easily adjustable.